Plunger assembly for a high-pressure fuel pump, and high-pressure fuel pump

ABSTRACT

The invention relates to a plunger assembly for a high-pressure fuel pump for supporting a reciprocating pump piston ( 1 ) of a pump element on a cam ( 2 ) of a drive shaft ( 3 ), comprising a supporting element ( 4 ) with a recess ( 5 ), in which a running roller ( 6 ) is mounted rotatably. According to the invention, it is provided that, furthermore, a holding element ( 7 ) is provided for holding the running roller ( 6 ) in the recess ( 5 ) of the supporting element ( 4 ), which holding element ( 7 ) is connected to the supporting element ( 4 ) in a positively locking manner, wherein the positively locking connection brings about an anti-rotation safeguard of the holding element ( 7 ) with respect to a longitudinal axis A of the pump piston ( 1 ).

BACKGROUND OF THE INVENTION

The present invention relates to a plunger assembly for a high-pressurefuel pump for supporting a reciprocatingly movable pump piston of a pumpelement on a cam of a drive shaft, comprising a support element with arecess in which a running roller is rotatably mounted . The inventionfurthermore relates to a high-pressure fuel pump having a plungerassembly of said type.

A plunger assembly of the above-mentioned type emerges for example fromDE 10 2008 000 699 A1. Said plunger assembly comprises a hollowcylindrical plunger body in which a roller shoe for the rotatablemounting of a running roller is accommodated. Via the running roller, apump piston of a pump element can be supported on a cam of a driveshaft, such that the pump piston is driven in a reciprocating movementwhen the drive shaft rotates. A restoring spring ensures the restoringmovement of the pump piston by virtue of the restoring spring beingsupported on a spring plate which is connected to the pump piston in aform-fitting manner. The form fit is realized by virtue of the springplate engaging behind a piston foot of the pump piston.

To prevent the running roller from rotating about the longitudinal axisof the pump piston during the operation of the high-pressure pump, it isproposed in DE 10 2008 000 699 A1 that one end of the restoring springbe connected to the roller shoe in a form-fitting manner. The preventionof rotation results in a uniform load on the running roller, such thatwear is reduced.

It is not only the running roller, but also those surfaces of the othercomponents of the plunger assembly that are in frictional contact withthe running roller, that are subject to wear. The present invention istherefore based inter alia on the object of specifying a plungerassembly with increased wear resistance.

SUMMARY OF THE INVENTION

The proposed plunger assembly comprises a support element with a recessin which a running roller is rotatably mounted. According to theinvention, it is provided that, to hold the running roller in the recessof the support element, provision is also made of a retention elementwhich is connected to the support element in a form-fitting manner.Here, the form fit has the effect of preventing rotation of theretention element with respect to a longitudinal axis A of the pumppiston.

The support and retention functions are conventionally performed by theroller shoe by virtue of the recess for the rotatable mounting of theroller having a wraparound angle of >180°. For the insertion of theroller into the roller shoe, said roller is pushed in from the side.After the roller shoe has been inserted into the hollow cylindricalplunger body, the running roller is securely held in the roller shoe,wherein the tips of the running roller bear against the inner wall ofthe plunger body. The inner wall of the plunger body accordingly formsaxial run-on surfaces for the running roller.

By contrast, in the plunger assembly according to the invention, thesupport and retention functions of the running roller are dividedbetween two elements, specifically the support element and the retentionelement. The wraparound angle of the recess of the support element mayaccordingly be selected to be <180°. The running roller is preventedfrom falling out of the recess of the support element by the retentionelement, wherein, to partially receive the running roller, the retentionelement has a recess whose width is selected to be smaller, at at leastone point, than the diameter of the running roller. The cross section ofthe recess is preferably matched to the cross section of the runningroller.

To prevent the retention element from rotating relative to the supportelement during the operation of the high-pressure pump, which in turncould lead to the running roller becoming jammed, the retention elementis connected to the support element in a form-fitting manner.

If it is thus ensured that the axial run-on surfaces for the runningroller are formed by the support element and/or the retention element, asleeve-shaped plunger body can be omitted. The running rolleraccordingly bears by way of its tips against delimiting surfaces of thesupport element and/or of the retention element. All of the surfacesthat are subjected to dynamic loading by the running movement of therunning roller are accordingly formed on the support element and/or onthe retention element, which may accordingly be produced from awear-resistant material and/or provided with a wear-resistant coating.Owing to the omission of the plunger body, the need for pressing thesupport element into the plunger body is also omitted. Since, during thepressing-in process, there is the risk of deformation of the supportelement and of the recess, formed therein, for receiving the runningroller, said risk is counteracted by dispensing with a plunger body.This has an advantageous effect on the running characteristics of therunning roller and thus the wear. The omission of the plunger bodyfurthermore results in a reduction of the weight of the plungerassembly, which has likewise proven to be expedient. This is because,owing to the weight reduction, it is firstly possible for the restoringspring to be of smaller dimensions, and secondly, the spacing betweenthe camshaft and the top side of the cylinder head can be reduced if theplunger assembly is used in a high-pressure fuel pump. This leads tofurther weight savings in the cylinder head and/or in the pump housing.

To realize the form fit between the retention element and the supportelement, it is proposed in one preferred embodiment of the inventionthat the retention element is at least partially inset into the supportelement. It may alternatively or additionally be provided that thesupport element has at least one axial projection which engages with theretention element. The form fit must be realized such that a rotation ofthe retention element with respect to the support element about thelongitudinal axis of the pump piston is counteracted.

As a refining measure, it is proposed that the axial projection isformed in the shape of a segment of a circle, and surrounds a partialcircumferential region of the retention element. Here, the axialprojection need not imperatively have been attached to the supportelement but rather may also have been produced by way of millingoperations. To produce multiple projections formed in the shape ofsegments of a circle, it is possible for the support element to haveinitially been milled out in circular form, for example, and for themilled-out portion to have been connected to the outer circumferentialsurface via radially running grooves. The grooves may interact withlugs, formed correspondingly thereto, of the retention element, suchthat a form fit is realized.

It is furthermore preferable for the retention element to be pressedinto the support element. In this way, the retention element is securedso as to be prevented from falling out if the form fit between theretention element and the support element serves merely for rotationprevention.

The retention element advantageously forms axial run-on surfaces for therunning roller. The running roller is accordingly secured in positionprimarily by the retention element. The wraparound angle of the runningroller may accordingly also be considerably less than 180°, for example140°.

In one refinement of the invention, it is proposed that the runningroller has planar tip surfaces by which the running roller bears againstthe retention element and/or against the support element. Owing to theareal contact instead of the conventional punctiform contact, it ispossible for much higher lateral run-on forces to be absorbed. Wear canbe further reduced in this way. Furthermore, a running roller with flattips is easier and accordingly cheaper to produce.

The high-pressure fuel pump which is also proposed for achieving theobject stated in the introduction and which has a plunger assemblyaccording to the invention is characterized in that the support elementof the plunger assembly is inserted directly into a housing bore of thehigh-pressure fuel pump. The support element is thus not received in ahollow cylindrical plunger body. The advantages associated with theomission of the plunger body have already been described above, suchthat reference is made to said part of the description.

It is also proposed that the retention element has a lug which protrudesradially in relation to the support element and which interacts with agroove of the housing bore so as to prevent rotation of the plungerassembly.

It is furthermore preferable for the plunger assembly to be connected tothe pump piston by means of a spring plate, wherein the spring plate ispressed onto the pump piston. In this way, the pump piston can be formedwithout a piston foot, which simplifies production.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be explained in more detailbelow on the basis of the appended drawings, in which:

FIG. 1 is a partial perspective sectional view of a known high-pressurepump in the region of a plunger assembly,

FIG. 2 shows a longitudinal section through a plunger assembly accordingto the invention,

FIG. 3 shows a view of the plunger assembly of FIG. 2 from below, and

FIG. 4 shows a longitudinal section through the support element, theretention element and the running roller of the plunger assembly ofFIGS. 2 and 3, the section plane having been rotated through 90° withrespect to the section plane of FIG. 2.

DETAILED DESCRIPTION

The high-pressure pump illustrated as a detail in the region of aplunger assembly in FIG. 1 comprises at least one pump element with areciprocatingly guided pump piston 1 which is supported, via a plungerassembly, on a cam 2 of a drive shaft 3. The plunger assembly isreceived in an axially displaceable manner in a housing bore 11 of ahousing part 20 of the high-pressure pump.

The illustrated plunger assembly comprises a sleeve-shaped plunger body13 and, received therein, a support element 4 with a recess 5 for therotatable mounting of a running roller 6. Via the running roller 6, theplunger assembly is supported directly on the outer circumference of thecam 2 of the drive shaft 3. A restoring spring 14 ensures the abutmentof the plunger assembly against the cam 2.

The restoring spring 14 and the support element 4 of the plungerassembly are supported in each case on opposite sides of an annularcollar 16 of the plunger body 13, wherein the restoring spring 14 issupported indirectly on the annular collar 16 via a spring plate 12. Thespring plate 12 serves for connecting the plunger assembly to the pumppiston 1. For this purpose, the spring plate 12 has a central recessthrough which the pump piston 1 is guided such that the spring plate 12engages behind a piston foot 15 of the pump piston 1. In this way, aform-fitting connection of the pump piston 1 to the plunger assembly isrealized.

The plunger assembly according to the invention illustrated in FIGS. 2to 4 differs from that in FIG. 1 in particular in that no plunger body13 is provided. The support element 4 is received directly in thehousing bore 11 of the housing part 20 of the high-pressure pump (seeFIG. 2). Furthermore, the support element 4 has a central milled-outportion which extends, via grooves 18, to the outer circumference of thesupport element 4 (see FIG. 3). The milled-out portion is delimited bytwo projections 8 which are in the form of segments of a circle, saidprojections being of rotationally symmetrical form and being separatedfrom one another by the grooves 18. Into the central milled-out portionthere is pressed a retention element 7 which has lugs 17 which engageinto the grooves 18 such that a form fit is produced (see FIGS. 3 and4). The lugs that engage with the grooves 18 thus prevent a rotation ofthe retention element 7 with respect to the support element 4 about thelongitudinal axis A of the pump piston 1.

By virtue of a lug 17 extending in a radial direction beyond the outercircumference of the support element 4 (see FIG. 4), said lug can beused for preventing rotation of the plunger assembly within the housingbore 11. For this purpose, a groove (not illustrated) which interactswith the lug 17 is formed in the housing bore 11.

As can also be seen from FIG. 4, the running roller 6 has planar tipsurfaces 10, that is to say flat tips by which the running roller 6bears against axial run-on surfaces 9 formed by the retention element 7(see FIGS. 3 and 4).

It can also be seen from FIG. 2 that the support element 4, theretention element 7 and the spring plate 12 have throughflow openings 19arranged to the sides of the running roller 6 (see also FIG. 3). Saidthroughflow openings ensure the throughflow of fuel.

Furthermore, the pump piston 1 is illustrated without a piston foot 15,from which it follows that the spring plate 12 is pressed onto the pumppiston 1. This is however not imperatively necessary. The pump piston 1may also be formed with a piston foot 15. That end of the pump piston 1which faces away from the spring plate 12 is received in a cylinder head21 of the high-pressure pump.

1. A plunger assembly for a high-pressure fuel pump for supporting areciprocatingly movable pump piston (1) of a pump element on a cam (2)of a drive shaft (3), comprising a support element (4) with a recess (5)in which a running roller (6) is rotatably mounted, also comprising, tohold the running roller (6) in the recess (5) of the support element(4), a retention element (7) which is connected to the support element(4) in a form-fitting manner to prevent rotation of the retentionelement (7) with respect to a longitudinal axis of the pump piston (1).2. The plunger assembly as claimed in claim 1, characterized in that, torealize a form fit, the support element (4) has at least one axialprojection (8) which engages with the retention element (7).
 3. Theplunger assembly as claimed in claim 2, characterized in that the axialprojection (8) is formed in the shape of a segment of a circle, andsurrounds a partial circumferential region of the retention element (7).4. The plunger assembly as claimed in claim 1, characterized in that theretention element (7) is pressed into the support element (4).
 5. Theplunger assembly as claimed in claim 1, characterized in that theretention element (7) forms axial run-on surfaces (9) for the runningroller (6).
 6. The plunger assembly as claimed in claim 1, characterizedin that the running roller (6) has planar tip surfaces (10) by which therunning roller (6) bears against at least one of the retention element(7) and the support element (4).
 7. A high-pressure fuel pump having aplunger assembly as claimed in claim 1, wherein the support element (4)is inserted directly into a housing bore (11) of the high-pressure fuelpump.
 8. The high-pressure fuel pump as claimed in claim 7,characterized in that the retention element (7) has a lug (17) whichprotrudes radially in relation to the support element (4) and whichinteracts with a groove of the housing bore (11) so as to preventrotation of the plunger assembly.
 9. The high-pressure fuel pump asclaimed in claim 7, characterized in that the plunger assembly isconnected to the pump piston (1) by means of a spring plate (12),wherein the spring plate (12) is pressed onto the pump piston (1). 10.The plunger assembly as claimed in claim 1, characterized in that, torealize a form fit, the retention element (7) is at least partiallyinset into the support element (4).
 11. The plunger assembly as claimedin claim 1, characterized in that, to realize the form fit, the supportelement (4) has at least one axial projection (8) which engages with theretention element (7).